Margaret Thatcher opened the centre in 1986 to be the shop window of UK horticulture.
The garden industry has given more than £500,000 in sponsorship in the past 22 years. Large show gardens, such as those from Marshalls, Stonemarket and Sunflower Street are on site.
The Enfield-based college is in discussion with HTA and HW publisher Haymarket about joint sponsorship of the centre.
The college is 20 minutes from the 2012 Olympic site in Stratford, and Capel Manor College chief executive Steve Dowbiggin sees its potential as a "must visit" attraction from 2011-13.
He said: "The NGC has been a huge success but it needs a makeover. One-third of the 34 gardens will be redesigned over the next two years. The industry is looking for a permanent showcase close to the Olympics so we can show visitors everything that's great about UK horticulture."
The college has spent £3m restoring the rest of its gardens. It aims to increase visitor numbers from 90,000 to 250,000 a year.Before 2011 it will spend £7.7m on refurbishing and extending Capel Manor, to include a new entrance to the gardens, along with better retail facilities and public catering.
The college is planning a special garden on the Olympic theme, designed by students using the five Olympic ruins as inspiration.
Estate manager Nick Evans said: "The college is looking to ensure that the gardens are developed so as to complement the significant investment planned at the NGC."
NGC senior gardener Julia Phipps said: "The HTA will be able to put us in touch with prospective sponsors who may wish to take advantage of opportunities."
The college will make £25,000 a year available for four years to attract top garden designers to build gardens at the NGC.
Haymarket publisher Richard Watts said: "We're actively investigating how we can work with the NGC to encourage visitors to the Olympics to see what fantastic gardening talent is available in this country."